Space Exploration Chronology: Extrasolar Planets: Gliese 581-g | HD 85512b | Kepler-10b | Kepler-22b



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Exoplanets (extrasolar planets) are planets located outside of our Solar System. Their existence has been debated for at hundreds of years, until first discovery was made in 1992. Everything that we see, is a reflection of light, consequently detecting a planet in other star systems is difficult, because planets are dim. Reflection from their parent stars present additional difficulties. The latter problem will be partially solved with a Terrestrial Planet Finder in 2023.
To-date, almost 700 exoplanets have been detected, including over 50 planetary systems. Full, daily updated, list of exoplanets can be found by at The Extrasolar Planets Encyclopaedia. Note that there are many websites presenting themselves as foremost databases on extrasolar planets, but they all get their statistics from this source. Astronomers are most interested in locating a terrestrial planet, composed of rocks and metals, within a habitable zone of its parent star. We believe that such planets are potentially Earth-like and could, in theory, host life and sentient species. Habitable Zone is a term used to describe a specific distance from the parent star in which conditions are faborable for liquid water to be present on the planet's surface. Earth is located in a Habitable Zone. As of September 2010, Astronomers have found a single, unconfirmed, Earth-like exoplanet, called Gliese 581 g.
On February 1, 2011 the Kepler Mission team had announced new, staggering statistics. They claimed to have discovered 5 Earth-size exoplanet candidates in habitable zones of their respective stars. Thus, the number of unconfirmed (none are confirmed, yet) Earth-like extrasolar planets has risen to 6. However, more surprises are left to be illuminated, as the Kepler scientists mentioned that a total of 54 exoplanet candidates have been discovered in habitable zones, their sizes range from super-Earth-size to Neptune size, large, planets. How many of them are super-Earth-size has not been revealed by NASA. These new findings could dramatically catapult the list of known Earth-like planets into double digits. What has been a subject of fictional speculation is now rapidly making its way into hard scientific data.
Probability dictates that soon we will discover numerous Earth-like exoplanets. This section of SpaceChronology will keep you updated on any and all Earth-like planets. Though most exoplanets, so far, have been detected using ground-based telescopes, space-based telescopes are required for greater accuracy and wider possibilities. In 2009, NASA launched The Kepler Telescope, specifically designed to detect Earth-like worlds.

Notable Earth-like and Earth-size planets:

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In September 2010 Gliese 581 g (Zarmina) First Earth-like candidate exoplanet, known to the Human race, is discovered (click on the text to read full report)


Click on the image to see it in full resolution.
Artwork credit: (c) Lynette Cook


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Earth-like planet, named HD 85512b, discovered 36 light years away in August 2011. The host star Gliese 370 is an orange solitary K5 V-type star, orbited by HD 85512b at 0.26 AU, placing it directly inside the star's habitable zone. Planetary mass is estimated to be at 3.6 0.5, which puts it in the Super-Earth category. The planet's orbital period is about 54 days. Surface temperature is estimated to be at 298 K (25 C or 77 F). Currently unknown climate condition, such as clouds, could significantly alter surface temperature. However, given the information currently available, it is very likely that liquid water could permenantly exist on the surface of HD 85512b, it could even dominate it.

The discovery was made by a Swiss team of Astronomers utilizing La Silla Observatory in Chile. It was detected using Radial velocity method.



This is an artist's vision of HD 85512b. Click on the image to see it in full resolution.
Credit: ESO


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On January 10, 2011 the Kepler Mission announced a confirmed discovery of
Kepler-10b, an extrasolar rocky planet, smallest ever discovered outside our Solar System.


Artist concept of Kepler 10b.
Credit: NASA.
Click on the image to see it in full resolution.


Kepler-10b is a rocky planet, like Earth, and is just 1.4 times the size of out planet, which makes it the smallest planet ever discovered outside our Solar System. The confirmation of discovery has been announced by the Kepler team after 8 months of observation. The orbit period of planet Kepler-10b is only 0.84 days, placing it 20 times closer to its star than Mercury is to our Sun. This rocky, Earth-size planet is not Earth-like, it is out the habitable zone; liquid water could not exist on its surface. Mass of Kepler-10b is 4.6 times that of Earth. Average density is 8.8 grams per cubic centimeter. The Kepler-10 planetary system is 560 light-years away from Earth. The host star is approximately 8 billion years old.(1)
Discovery of Kepler-10b is an important milestone because it illuminates the optimistic prospects of discovering an Earth-size planet in a habitable zone of its star. It is also a vital confirmation of successful implementation and use of the Kepler Mission designated instrumentation in the search for planets similar to our own, elsewhere in the Galaxy.
Potential presence of a small planet in Kepler-10 star system was recognized as early as May 2009 and was submitted for ground-based confirmation by the W.M. Keck Observatory 10-meter telescope in Hawaii. NOTE: Kepler Mission has now discovered over 700 exoplanet candidates, however, their existence has to be confirmed by months of observations. Finds such as this are expected to become common in the coming months to years.
Kepler Mission Official Parameters of Kepler-10b exoplanet



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The Mysterious Unconfirmed 5 Earth-Like Exoplanets

In February 2011 Kepler Mission scientists announced a discovery of 5 Earth-size exoplanets in habitable zones of their respective stars. This raises the number of potential Earth-like extrasolar planets to 6, including the Gliese 581 g. Because of the unconfirmed nature of these planets, NASA is withholding any additional information. In any case, this dramatically raises our expectations on the amount of Earth-like planets that we will discover and confirm in the near future. American scientists at the Kepler Mission have also disclosed that a total of 54 planet candidates have been discovered in habitable zones, many of them could be super-Earth-size or gas giants with numerous moons with Earth-like environments orbiting around them.(2)

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Earth-like exoplanet discovered & confirmed: Kepler-22b

On December 5, 2011 the NASA Kepler Mission, charged with the search for Earth-like planets, announced the discovery of Kepler-22b. It orbits a similar star to our own, located 600 light years away from us, in its respective habitable zone, just like Earth orbits in the habitable zone of our Sun. Kepler-22b has 2.4 the radius of Earth, it falls under the classification of a Super-Earth. Unlike Gliese 581 g, the existence of Kepler-22b is proven beyond doubt by the Kepler NASA team.

Artist's comparison of our Solar System's habitable zone with that of Kepler-22.
Image credit: NASA/Ames/JPL-Caltech
Click on the image to see it in full resolution.



The chemical composition of the planet has not been determined. There is a chance this this is not a terrestrial planet (like Earth, Mars, Venus, and Mercury) but gaseous or liquid. Thus, it is yet impossible to say how truly Earth-like Kepler-22b is, but its location and size proves that in the future we will discover numerous exoplanets resembling our Earth in extreme detail. The fact that Kepler-22b is 600 light years away from Earth, sending an interstellar probe is out of the question with the available propulsion technology.

Artist's concept of Kepler 22b.
Image credit: NASA/Ames/JPL-Caltech
Click on the image to see it in full resolution.


Documentary in HD quality on exoplanets in general by JPL/Caltech:





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Sources
  1. NASA'S Kepler Mission Discovers Its First Rocky Planet
  2. NASA Finds Earth-size Planet Candidates in Habitable Zone

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